U.S. patent number 6,991,579 [Application Number 10/271,729] was granted by the patent office on 2006-01-31 for toroidal type continuously variable transmission.
This patent grant is currently assigned to NSK Ltd.. Invention is credited to Hideki Hashitani, Takashi Imanishi, Norihisa Kobayashi, Shinji Miyata.
United States Patent |
6,991,579 |
Kobayashi , et al. |
January 31, 2006 |
Toroidal type continuously variable transmission
Abstract
A toroidal type continuously variable transmission having first
and second discs supported around a rotating shaft and receiving
power rollers therebetween includes a ball spline having a first
spline groove formed in an outer circumferential surface of the
rotating shaft, a second spline groove formed in an inner
circumferential surface of the first disc, and balls provided
between the first spline groove and the second spline groove
rollably. An axial position of an end portion of an effective
groove portion of the first spline groove is located to correspond
to an axial position of an inner end portion of the second spline
groove or more closely to the second disc than the axial position
thereof when a pressing unit, a preload spring and the first disc
are installed around the rotating shaft, pressure oil is not fed to
the pressing unit, and the preload spring is not elastically
deformed.
Inventors: |
Kobayashi; Norihisa (Kanagawa,
JP), Miyata; Shinji (Kanagawa, JP),
Imanishi; Takashi (Kanagawa, JP), Hashitani;
Hideki (Kanagawa, JP) |
Assignee: |
NSK Ltd. (Tokyo,
JP)
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Family
ID: |
19139401 |
Appl.
No.: |
10/271,729 |
Filed: |
October 17, 2002 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20030078133 A1 |
Apr 24, 2003 |
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Foreign Application Priority Data
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Oct 19, 2001 [JP] |
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2001-322335 |
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Current U.S.
Class: |
476/42;
476/45 |
Current CPC
Class: |
F16H
15/38 (20130101); F16H 61/6649 (20130101) |
Current International
Class: |
F16H
15/38 (20060101) |
Field of
Search: |
;476/40,42,45,46 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2-283949 |
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Nov 1990 |
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JP |
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6-14604 |
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Feb 1994 |
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JP |
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6-37222 |
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Sep 1994 |
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JP |
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6-280957 |
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Oct 1994 |
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JP |
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8-4869 |
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Jan 1996 |
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JP |
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8-61453 |
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Mar 1996 |
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JP |
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9-88988 |
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Mar 1997 |
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JP |
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10-159926 |
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Jun 1998 |
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JP |
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11-51135 |
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Feb 1999 |
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JP |
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2595141 |
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Mar 1999 |
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JP |
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11-141564 |
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May 1999 |
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JP |
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11-182644 |
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Jul 1999 |
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JP |
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11-241754 |
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Sep 1999 |
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JP |
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11-247953 |
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Sep 1999 |
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JP |
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2000-18350 |
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Jan 2000 |
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JP |
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2000-199553 |
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Jul 2000 |
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JP |
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2000-213610 |
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Aug 2000 |
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JP |
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2000-233367 |
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Aug 2000 |
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JP |
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2000-240748 |
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Sep 2000 |
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JP |
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2000-291756 |
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Oct 2000 |
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JP |
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2001-027298 |
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Jan 2001 |
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JP |
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2001-124165 |
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May 2001 |
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JP |
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Other References
Nikkei Mechanical vol. 564, (Sep. No. 2001), pp. 76-77, published
by Nikkei Business Publications Inc., Sep. 1, 2001, is discussed on
p. 8 in the specification for the above application. cited by
other.
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Primary Examiner: Fenstermacher; David
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A toroidal type continuously variable transmission comprising: a
rotating shaft; a pair of first discs each having an inner side
surface and supported around said rotating shaft displaceably in an
axial direction of said rotating shaft and rotatably in sync with
said rotating shaft; a second disc having an inner side surface
opposed to said inner side surface of one of said first discs and
disposed concentrically with said first disc and rotatably
independently of said first discs; a plurality of trunnions
provided between said first and second discs so as to swing around
pivot shafts located in twisted positions with respect to central
axes of said two discs, respectively; displacement shafts
projecting from inner side surfaces of said trunnions; power
rollers sandwiched between said inner side surfaces of said first
and second discs so as to be supported on said displacement shafts
rotatably, respectively; a hydraulic pressing unit provided between
said rotating shaft and said one of said first discs and for
pressing said one of said first discs toward said second disc in
accordance with pressure oil fed to said pressing unit; a preload
spring provided between said rotating shaft and said one of said
first discs and for pressing said one of said first discs toward
said second disc even when said pressing unit is not operated; and
a ball spline for supporting said one of said first discs
displaceably in said axial direction of said rotating shaft and
rotatably in sync with said rotating shaft, wherein said ball
spline includes a first spline groove formed in an outer
circumferential surface of said rotating shaft, a second spline
groove formed in an inner circumferential surface of said one of
said first discs, and balls provided between said first spline
groove and said second spline groove rollably; and wherein an axial
position of an end portion of an effective groove portion of said
first spline groove is located so as to correspond to an axial
position of an inner end portion of said second spline groove or is
located more closely to said second disc than is said axial
position of said inner end portion, wherein the locations of said
effective groove portion and said inner end portion are determined
when said pressing unit, said preload spring and said one of said
first discs are installed around said rotating shaft, pressure oil
is not fed to said pressing unit, and said preload spring is not
elastically deformed.
2. The toroidal type continuously variable transmission according
to claim 1, wherein said hydraulic pressing unit includes at least
one piston member.
3. The toroidal type continuously variable transmission according
to claim 1, wherein said first spline groove has said effective
groove portion having a constant depth, and imperfect groove
portions getting gradually shallower from opposite end portions of
said effective groove.
4. The toroidal type continuously variable transmission according
to claim 1, wherein the preload spring is provided in the hydraulic
pressing unit.
5. The toroidal type continuously variable transmission according
to claim 1, wherein the hydraulic pressing unit comprises a first
piston and a second piston.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toroidal type continuously
variable transmission, which is used as a transmission unit
constituting an automobile automatic transmission unit or as a
transmission for regulating the running speed of various industrial
machines such as a pump.
2. Description of the Related Art
Toroidal type continuously variable transmissions have been known
as a kind of transmission unit constituting an automobile
transmission. Some toroidal type continuously variable
transmissions have been put into practical use. Such toroidal type
continuously variable transmissions already put into practical use
are heretofore known well as disclosed in a large number of
official gazettes such as U.S. Pat. No. 5,033,322, U.S. Pat. No.
5,569,112 and U.S. Pat. No. 5,651,750. A basic structure of such a
toroidal type continuously variable transmission will be described
with reference to FIG. 3. The structure shown in FIG. 3 is a
so-called double-cavity type in which power transmission from an
input portion to an output portion is carried out by two systems
separated in parallel with each other. In contrast, a so-called
single-cavity type toroidal type continuously variable transmission
in which power transmission is carried out by only one system is
also known well as disclosed in a large number of official
gazettes. In the case of the double-cavity type toroidal type
continuously variable transmission shown in FIG. 3, an input-side
disc 2a which is a first disc is supported around an input-side
rotating shaft 1 in a portion close to the base end (to the left of
FIG. 3) with respect to an intermediate portion of the input-side
rotating shaft 1. The input-side rotating shaft 1 corresponds to a
rotating shaft. On the other hand, the other input-side disk 2b is
supported around the input-side rotating shaft 1 in a portion close
to its forward end (to the right of FIG. 3). The input-side discs
2a and 2b are supported through ball splines 4 and 4 so that
input-side inner side surfaces 3 and 3 which are toroidal surfaces
respectively are opposed to each other. Accordingly, both the
input-side discs 2a and 2b are supported around the input-side
rotating shaft 1 displaceably in the axial direction of the
input-side rotating shaft 1 and rotatably in sync with the
input-side rotating shaft 1.
Each of the ball splines 4 and 4 is formed by providing a plurality
of balls 7 and 7 between first and second spline grooves 5 and 6
rollably. The first spline grooves 5 and 5 are formed in the outer
circumferential surface of the input-side rotating shaft 1
respectively. On the other hand, the second spline grooves 6 and 6
are formed in the inner circumferential surfaces of the input-side
discs 2a and 2b respectively. In addition, a rolling bearing 8 and
a loading cam style pressing unit 9 are provided between the base
end portion of the input-side rotating shaft 1 and the outer side
surface of the input-side disc 2a which is a first disc. Then, a
cam plate 10 constituting the pressing unit 9 can be driven to
rotate desirably by a drive shaft 11. On the other hand, a loading
nut 12 and a coned disk spring 13 having great elastic force are
provided between the forward end portion of the input-side rotating
shaft 1 and the outer side surface of the other input-side disc
2b.
The intermediate portion of the input-side rotating shaft 1
penetrates a through hole 15 provided in a partition portion 14
provided in a casing receiving the toroidal type continuously
variable transmission. A cylindrical sleeve 16 is supported on the
inner diameter side of the through hole 15 rotatably by a pair of
rolling bearings 17 and 17. An output gear 18 is fixedly provided
on the outer circumferential surface of an intermediate portion of
the sleeve 16. In addition, output-side discs 19a and 19b are
supported on opposite end portions of the sleeve 16 which project
from the opposite outer side surfaces of the partition portion 14,
respectively. The output-side discs 19a and 19b are made rotatable
in sync with the sleeve 16 by spline engagement. In this state,
output-side inner side surfaces 20 and 20 of the output-side discs
19a and 19b which are toroidal surfaces respectively face the
input-side inner side surfaces 3 and 3 respectively. In addition,
needle roller bearings 21 and 21 are provided between the outer
circumferential surface of the intermediate portion of the
input-side rotating shaft 1 and portions of the inner
circumferential surfaces of the output-side discs 19a and 19b
projecting from the edge of the sleeve 16, respectively. Thus, the
needle roller bearings 21 and 21 bear loads on the output-side
disks 19a and 19b respectively while allowing the output-side disks
19a and 19b to make rotation and axial displacement with respect to
the input-side rotating shaft 1. Incidentally, of the output-side
discs 19a and 19b, the output-side disc 19a close to the pressing
unit 9 (to the left of FIG. 3) corresponds to a second disc.
In addition, a plurality (typically two or three) of power rollers
22 and 22 are disposed around the input-side rotating shaft 1 and
in each space (cavity) between the input-side and output-side inner
side surfaces 3 and 20. The power rollers 22 and 22 have
spherically convex surfaces in their circumferential surfaces in
contact with the input-side and output-side inner side surfaces 3
and 20, respectively. The power rollers 22 and 22 are supported on
the inner side surface portions of trunnions 23 and 23 through
displacement shafts 24 and 24, radial needle roller bearings 25 and
25, thrust ball bearings 26 and 26, and thrust needle roller
bearings 27 and 27 so as to be allowed to make rotation and slight
swinging displacement. That is, the displacement shafts 24 and 24
are eccentric shafts each having a base half portion and a forward
half portion eccentric to each other. Then, the base half portions
of the displacement shafts 24 and 24 are supported on the
intermediate portions of the trunnions 23 and 23 through other
radial needle roller bearings (not shown) so as to be allowed to
make swinging displacement, respectively.
The power rollers 22 and 22 are supported rotatably on the forward
half portions of the displacement shafts 24 and 24 through the
radial needle roller bearings 25 and 25 and the thrust ball
bearings 26 and 26, respectively. In addition, the displacements of
the power rollers 22 and 22 with respect to the axial direction of
the input-side rotating shaft 1, which are based on the elastic
deformations of the respective constituent members, are allowed
desirably by the other radial needle roller bearings and the thrust
needle roller bearings 25 and 25, respectively. Further, the
trunnions 23 and 23 are supported displaceably clockwise and
counterclockwise in FIG. 3 by pivot shafts provided in their
opposite end portions (in the front/back direction of FIG. 3),
respectively. At the same time, the trunnions 23 and 23 are made
displaceable in the axial direction (the front/back direction of
FIG. 3) of the pivot shafts by actuators (not shown), respectively.
In this connection, the pivot shafts are arranged in a physical
relationship such that the pivot shafts extend on a plane
perpendicular to the center axes of the input-side discs 2a and 2b
and the output-side discs 19a and 19b but does not intersect the
center axes thereof. Such a physical relationship is referred to as
"twisted position".
When the toroidal type continuously variable transmission
configured thus is operated, the input-side disc 2a corresponding
to the first disc is driven to rotate by the drive shaft 11 through
the pressing unit 9. The pressing unit 9 drives and rotates the
input-side disc 2a while generating axial thrust. Accordingly, the
pair of input-side discs 2a and 2b including the input-side disc 2a
rotate synchronously with each other while being pressed toward the
output-side discs 19a and 19b, respectively. As a result, the
rotations of the input-side discs 2a and 2b are transmitted to the
output-side discs 19a and 19b through the power rollers 22 and 22
respectively. Thus, the output gear 18 linked with the output-side
discs 19a and 19b through the sleeve 16 is rotated.
When the toroidal type continuously variable transmission is
operated, the surface pressures in respective contact portions
between the circumferential surfaces of the power rollers 22 and 22
and the input-side and output-side inner side surfaces 3 and 20 are
secured by the thrust generated by the pressing unit 9. In
addition, the greater the power (torque) transmitted from the drive
shaft 11 to the output gear 18 is, the higher the surface pressures
are. Accordingly, excellent transmission efficiency can be obtained
regardless of the change of the torque. In addition, even when the
torque to be transmitted is 0 or slight, the surface pressures in
the respective contact portions are secured to some extent by a
preload spring 28 provided on the inner diameter side of the
pressing unit 9. Thus, the torque transmission in the respective
contact portions is carried out smoothly without excessive slippage
on and after the start-up of the toroidal type continuously
variable transmission.
When the gear ratio between the drive shaft 11 and the output gear
18 is changed, the trunnions 23 and 23 are displaced in the
front/back direction of FIG. 3 by actuators (not shown). In this
case, the trunnions 23 and 23 in the upper half portion of FIG. 3
and the trunnions 23 and 23 in the lower half portion of FIG. 3 are
displaced in the directions opposite to each other and by the same
quantity. With this displacement, the directions of forces applied
tangentially to the contact portions between the circumferential
surfaces of the power rollers 22 and 22 and the input-side and
output-side inner side surfaces 3 and 20 are changed respectively.
Then, the tangential forces make the trunnions 23 and 23 swing
around the pivot shafts provided in their opposite end portions,
respectively. With the swinging motions, the contact portions
between the circumferential surfaces of the power rollers 22 and 22
and the input-side and output-side inner side surfaces 3 and 20
change their positions with respect to the radial directions of the
inner side surfaces 3 and 20, respectively. As the contact portions
are displaced to the axial outside of the input-side inner side
surface 3 and to the axial inside of the output-side inner side
surface 20 respectively, the gear ratio is changed to the speed
increasing side. On the contrary, as the contact portions are
displaced to the axial inside of the input-side inner side surface
3 and to the axial outside of the output-side inner side surface 20
respectively, the gear ratio is changed to the speed reducing
side.
In the case of the related-art structure, a mechanical loading cam
unit is used as the pressing unit 9 for securing surface pressures
in the respective contact portions between the circumferential
surfaces of the power rollers 22 and 22 and the input-side and
output-side inner side surfaces 3 and 20. In the case of such a
mechanical pressing unit 9, the surface pressures can be indeed
adjusted in accordance with the torque to be transmitted, but the
surface pressures cannot be adjusted in accordance with any other
element. In order to further improve the transmission efficiency
and the durability of the toroidal type continuously variable
transmission, it can be, for example, considered that the surface
pressures are changed in accordance with the change of temperature
causing the change of viscosity of traction oil. Further, in order
to realize a continuously variable transmission unit in which a
toroidal type continuously variable transmission and a planetary
gear mechanism are used in combination, it is necessary to adjust
the surface pressures in accordance with not only torque but also
other elements.
For example, as such a continuously variable transmission unit, a
continuously variable transmission unit called a power split type,
which can improve the transmission efficiency and the durability at
the time of high speed operation dramatically, has been known in
the related art as disclosed in not only a large number of patent
publications but also the technical magazine "Nikkei Mechanical"
Vol. 564 (September Number 2001), pp. 76 77, published by Nikkei
Business Publications Inc., Sep. 1, 2001. In addition, a
continuously variable transmission unit called a geared neutral
type has been also known in the related art as disclosed in a large
number of patent publications. In the geared neutral transmission
unit, a toroidal type continuously variable transmission and a
planetary gear mechanism are used in combination so that the
rotational velocity of an output shaft can be reduced to zero while
an input shaft is left rotating. In the case of such a continuously
variable transmission unit, mode selection among a plurality of
modes including a low-speed mode and a high-speed mode is
performed. In order to solve or relieve uncomfortable feeling given
to a driver at the time of the mode selection, it is effective that
the thrust generated by a pressing unit at the time of the mode
selection is adjusted separately from the torque.
On such an occasion, a structure shown in FIG. 4 is effective. The
invention relates to the improvement of the structure shown in FIG.
4. Therefore, first, description will be made on the structure
shown in FIG. 4. The structure shown in FIG. 4 is of a
double-cavity type in which a total of four power rollers are
provided so that two of them are disposed between the inner side
surfaces of a pair of input-side and output-side discs while the
other two are disposed between the inner side surfaces of the other
pair of input-side and output-side discs. On the other hand, there
is also a double-cavity type structure of the invention in which a
total of six power rollers are provided so that three of them are
disposed between the inner side surfaces of a pair of input-side
and output-side discs while the other three are disposed between
the inner side surfaces of the other pair of input-side and
output-side discs. However, such a structural difference is not
essential to the invention. The invention is applicable not only to
the structure shown in FIG. 4 but also to the structure in which a
total of six power rollers are provided. Further, the invention is
also applicable to a single-cavity type structure in which two or
three power rollers are provided between the inner side surfaces of
a pair of input-side and output-side discs.
In the case of the structure shown in FIG. 4, a pair of input-side
discs 2a and 2b are supported on the opposite end portions of an
input-side rotating shaft 1a corresponding to a rotating shaft, so
that the input-side discs 2a and 2b can rotate synchronously with
the input-side rotating shaft 1a while input-side inner side
surfaces 3 and 3 of the input-side discs 2a and 2b are opposed to
each other. Of them, the input-side disc 2a on the forward end side
(a side more distant from a drive source and on the right of FIG.
4) corresponding to a first disc is supported on the forward end
portion of the input-side rotating shaft 1a through a ball spline
4a displaceably axially and rotatably in sync with the input-side
rotating shaft 1a. On the other hand, the input-side disc 2b on the
base end side (a side closer to the drive source and on the left of
FIG. 4) is fixed to the input-side rotating shaft 1a in the
following manner. That is, in the state in which the input-side
disc 2b is spline-engaged with the base end portion of the
input-side rotating shaft 1a, the back surface of the input-side
disc 2b is held down by a loading nut 12a. Incidentally, a shim
plate 29 is sandwiched between the loading nut 12a and the
input-side disc 2b. As the shim plate 29, one with a proper
thickness selected from a plurality of kinds of shim plates
different in thickness is used to adjust the elastic force of a
coned disk spring 30 corresponding to a preload spring. The coned
disk spring 30 is built in a hydraulic pressing unit, which will be
described later, so as to provide preload.
Then, a pair of output-side discs 19a and 19b are supported around
the intermediate portion of the input-side rotating shaft 1a and
between the pair of input-side discs 2a and 2b so that the
output-side discs 19a and 19b can rotate synchronously with each
other while output-side inner side surfaces 20 and 20 of the
output-side discs 19a and 19b are opposed to the input-side inner
side surfaces 3 and 3 of the input-side discs 2a and 2b. In
addition, power rollers 22 and 22 are sandwiched between the
input-side inner side surfaces 3 of the input-side discs 2a and 2b
and the output-side inner side surfaces 20 of the output-side discs
19a and 19b, respectively, so as to be supported rotatably on the
inner side surfaces of trunnions 23 and 23. In the case of the
structure shown in FIG. 4, the structure for supporting the power
rollers 22 and 22 on the inner side surfaces of the trunnions 23
and 23 respectively and the structure for supporting the trunnions
23 and 23 swingably and axially displaceably in a casing are the
same as structures well known in the related art, including the
structure shown in FIG. 3, as will be described later.
In addition, an output sleeve 32 is disposed inside a casing (not
shown) provided for receiving the toroidal type continuously
variable transmission and on the inner diameter side of a gear
housing 31 provided between the pair of output-side discs 19a and
19b so as to be supported rotatably by a pair of rolling bearings
33 and 33. Then, an output gear 18a fixedly provided on the outer
circumferential surface of the intermediate portion of the output
sleeve 32 is supported rotatably in the gear housing 31. In
addition, curved engagement in the radial direction is made between
the axially opposite edge portions of the output sleeve 32 and
near-to-inner circumference portions of the outer side surfaces of
the output-side discs 19a and 19b so as to link the output-side
discs 19a and 19b with the output gear 18a rotatably in sync with
each other, respectively. In addition, needle roller bearings 21a
and 21a are provided between the inner circumferential surfaces of
the output-side discs 19a and 19b and the outer circumferential
surface of the intermediate portion of the input-side rotating
shaft 1a, respectively. Thus, the output-side discs 19a and 19b are
supported around the input-side rotating shaft 1a rotatably with
respect to the input-side rotating shaft 1a and displaceably in the
axial direction thereof.
In addition, the power rollers 22 and 22 disposed around the
input-side rotating shaft 1a and two by two between the input-side
and output-side inner side surfaces 3 and 20 are supported on the
inner side surface portions of the trunnions 23 and 23 through
displacement shafts 24 and 24, radial needle roller bearings 25 and
25, thrust ball bearings 26 and 26, and thrust needle roller
bearings 27 and 27 so as to be allowed to make rotation and slight
swinging displacement, respectively. Further, the trunnions 23 and
23 are supported displaceably clockwise and counterclockwise in
FIG. 4 by pivot shafts provided in their opposite end portions, and
displaceably in the axial directions of the pivot shafts by
actuators (not shown), respectively. Then, the circumferential
surfaces of the power rollers 22 and 22 are brought into contact
with the input-side and output-side inner side surfaces 3 and 20 of
the discs 2a, 2b, 19a and 19b respectively. In addition, a
hydraulic pressing unit 34 is installed between the input-side disc
2a on the forward end side and the input-side rotating shaft 1a so
as to secure the surface pressures in the contact portions
(traction portions) between the inner side surfaces 3 and 20 and
the circumferential surfaces of the power rollers 22 and 22. Thus,
the power can be transmitted efficiently by the toroidal type
continuously variable transmission.
To construct the pressing unit 34, an outward flange portion 35 is
fixedly provided in a near-to-forward end portion of the outer
circumferential surface of the input-side rotating shaft 1a. In
addition, a cylinder 36 is oil-tightly outer-fitted to the
input-side-disc 2a on the forward end side. Thus, the cylinder 36
is supported to project axially from the outer side surface (right
surface in FIG. 4) of the input-side disc 2a. The inner diameter of
the cylinder 36 is smaller in its axially intermediate portion and
larger in its opposite end portions. The input-side disc 2a is
inner-fitted to the base-end-side larger diameter portion of the
cylinder 36 oil-tightly and axially displaceably. In addition, an
inward-flange-like partition plate portion 37 is provided on the
inner circumferential surface of the intermediate portion of the
cylinder 36. Further, a first piston member 38 is provided between
the inner circumferential surface of the cylinder 36 and the outer
circumferential surface of the input-side rotating shaft 1a.
In the first piston member 38, an outward-flange-like partition
plate 40 is formed on the outer circumferential surface of the
intermediate portion of a support cylinder portion 39 which can be
outer-fitted to the input-side rotating shaft 1a. The outer
circumferential edge of the partition plate 40 is made to abut and
slide on the smaller-diameter portion of the intermediate portion
of the inner circumferential surface of the cylinder 36 oil-tightly
and axially displaceably. In addition, in this state, the inner
circumferential edge of the partition plate portion 37 is made to
abut and slide on the outer circumferential surface of the support
cylinder portion 39 oil-tightly and axially displaceably. Further,
a ring-like second piston member 41 is provided between the outer
circumferential surface of the forward end portion of the support
cylinder portion 39 and the inner circumferential surface of the
forward end portion of the cylinder 36. The second piston member 41
brings its forward-end-side side surface into contact with the
outward flange portion 35 so as to prevent axial displacement,
while keeping oil tightness between the inner circumferential edge
of the second piston member 41 and the outer circumferential
surface of the forward end portion of the support cylinder portion
39 and between the outer circumferential edge of the second piston
member 41 and the inner circumferential surface of the forward end
portion of the cylinder 36.
In addition, the cylinder 36 provided with the partition plate
portion 37 is pressed onto the input-side disc 2a by a coned disk
spring 30 provided between the partition plate portion 37 and the
second piston member 41. Accordingly, the input-side disc 2a is
pressed by at least the pressing force corresponding to the elastic
force of the coned disk spring 30 (even if pressure oil has not
been introduced into the pressing unit 34). Thus, surface pressure
corresponding to the elastic force is applied to the contact
portions between the input-side and output-side inner side surfaces
3 and 20 and the circumferential surfaces of the power rollers 22
and 22. Thus, the elastic force is regulated not to produce
slippage (excluding unavoidable spin) in the contact portions
between the input-side and output-side inner side surfaces 3 and 20
and the circumferential surfaces of the power rollers 22 and 22
when very small power is transmitted by the toroidal type
continuously variable transmission.
The elastic force of the coned disk spring 30 is adjusted for such
a purpose. The adjustment is carried out by changing the thickness
of the shim plate 29 sandwiched between the loading nut 12a and the
input-side disc 2b. That is, the outer diameter of a male thread
portion 42 formed in the base end portion of the input-side
rotating shaft 1a in order to screw down the loading nut 12a is
smaller than the outer diameter of a first spline portion 43
locking up the input-side disc 2b. Accordingly, there is a step
between the first spline portion 43 and the male thread portion 42.
When the toroidal type continuously variable transmission is
assembled, the loading nut 12a is screwed down to the male thread
portion 42 till it abuts against the step, and further secured. In
this state, as the shim plate 29, one with a proper thickness is
selectively used to set the elastic force of the coned disk spring
30 at a value proper to provide preload. Incidentally, the
thickness of the shim plate 29 is selected to prevent the coned
disk spring 30 from being completely compressed (prevent the coned
disk spring 30 from being perfectly flat) in the state in which the
loading nut 12a has been secured. Accordingly, there is no fear
that the surface pressures in the contact portions between the
input-side and output-side inner side surfaces 3 and 20 and the
circumferential surfaces of the power rollers 22 and 22 become
excessive as the loading nut 12a is secured. Hence, damage such as
impressions on those surfaces can be surely prevented from being
caused.
In addition, oil pressure is introduced desirably into a first oil
pressure chamber 44 and a second oil pressure chamber 45 through a
central hole 46 of the input-side rotating shaft 1a. The first oil
pressure chamber 44 is provided between the partition plate 40 and
the input-side disc 2a, and the second oil pressure chamber 45 is
provided between the second piston member 41 and the partition
plate portion 37. To this end, the deep end portion of the central
hole 46 and the outer circumferential surface of the intermediate
portion of the input-side rotating shaft 1a are brought into
communication with each other through branch holes 47 and 47 formed
radially in the intermediate portion of the input-side rotating
shaft 1a. In addition, an annular recess portion 48 is formed all
over the circumference of a portion of the inner circumferential
surface of the support cylinder portion 39 corresponding to the
outer-diameter-side openings of the branch holes 47 and 47.
Further, first and second communication holes 49 and 50 are
provided so that their one ends communicate with the annular recess
portion 48 while the other ends communicate with the first and
second oil pressure chambers 44 and 45 respectively. On the other
hand, the central hole 46 communicates with an oil pressure source
such as a pressure pump (not shown) through an oil pressure control
valve (not shown). When the toroidal type continuously variable
transmission is operated, oil pressure controlled by the oil
pressure control valve in accordance with the magnitude of power to
be transmitted or the state of mode selection is introduced into
the first and second oil pressure chambers 44 and 45 so as to press
the input-side disc 2a. Thus, surface pressures corresponding to
the magnitude of power to be transmitted or the state of mode
selection are given to the contact portions between the input-side
and output-side inner side surfaces 3 and 20 and the
circumferential surfaces of the power rollers 22 and 22
respectively.
Further, in the illustrated example, the rotational force is
transmitted from a drive shaft 51 to the input-side rotating shaft
1a through the input-side disc 2b supported on the base end portion
of the input-side rotating shaft 1a. To this end, a plurality of
protrusion portions 52 and 52 are provided to project over a half
portion of the outer side surface (left surface in FIG. 4) of the
input-side disc 2b radially closer to the outer diameter portion of
the outer side surface than to the central portion thereof. The
protrusion portions 52 and 52 are formed into arcs respectively,
and disposed intermittently and at an equal interval on the same
arc around the central axis of the input-side disc 2b. Then, lock
notch portions 53 and 53 are formed between circumferential end
surfaces of circumferentially adjacent ones of the protrusion
portions 52 and 52. To say other words, short cylindrical portions
provided to project over the outer side surface of the input-side
disc 2b are removed at an equal interval so as to form the lock
notch portions 53 and 53. Thus, the protrusion portions 52 and 52
are formed between circumferentially adjacent ones of the lock
notch portions 53 and 53.
On the other hand, a transmission flange 55 is provided in the
forward end portion of the drive shaft 51 through a transmission
cylinder portion 54 shaped like a conical cylinder. Then,
transmission projections 56 and 56 equal in number to the lock
notch portions 53 and 53 are circumferentially formed in the outer
circumferential edge portion of the transmission flange 55 at an
equal interval. Then, the transmission projections 56 and 56 and
the lock notch portions 53 and 53 are engaged with each other so
that torque can be transmitted between the input-side disc 2b and
the drive shaft 51. The diameter of each of engagement portions
between the transmission projections 56 and 56 and the lock notch
portions 53 and 53 is large enough so that sufficiently large
torque can be transmitted desirably between the drive shaft 51 and
the input-side disc 2b.
The basic operation for the toroidal type continuously variable
transmission having a structure formed the above to transmit power
between the drive shaft 51 and the output gear 18a is similar to
that for a toroidal type continuously variable transmission which
is known broadly in the related art including the structure shown
in FIG. 3. Particularly, in the case of the toroidal type
continuously variable transmission shown in FIG. 4, the hydraulic
pressing unit 34 is used. Accordingly, the surface pressures in the
contact portions between the input-side and output-side inner side
surfaces 3 and 20 and the circumferential surfaces of the power
rollers 22 and 22 can be controlled not only in accordance with the
torque to be transmitted but also in accordance with the
temperature or the state of mode selection of a continuously
variable transmission unit in which the toroidal type continuously
variable transmission has been incorporated. Accordingly, not only
is it possible to further improve the efficiency of the toroidal
type continuously variable transmission but it is also possible to
make control to suppress a sudden change of elastic deformation
quantity in each constituent member caused by mode selection so as
to suppress the fluctuation of the gear ratio caused by the sudden
change.
When the structure shown in FIG. 4 is assembled, the work of
assembling the ball spline 4a for supporting the input-side disc 2a
in the forward end portion of the input-side rotating shaft 1a
becomes troublesome unless the shapes of the respective portions
are devised. Accordingly, the manufacturing cost of the toroidal
type continuously variable transmission increases. Description
about this reason will be made with reference to FIGS. 5A and 5B
and FIG. 6 as well as FIG. 4.
When the toroidal type continuously variable transmission shown in
FIG. 4 is assembled, the constituent members of the hydraulic
pressing unit 34, that is, the cylinder 36, the first and second
piston members 38 and 41, and the coned disk spring 30 are
assembled in advance. Then, the hydraulic pressing unit 34 is
outer-fitted to the inside portion of the outward flange portion 35
in the forward end portion of the input-side rotating shaft 1a.
Next, as shown in FIG. 5A, the input-side disc 2a is outer-fitted
to a near-to-forward end portion of the input-side rotating shaft
1a, while the outer circumferential edge portion of the input-side
disc 2a is inner-fitted to the cylinder 36. After the respective
members 1a, 36, 38, 41 and 30 are assembled as shown in FIG. 5A,
the balls 7 and 7 constituting the ball spline 4a are incorporated
between the first spline groove 5 formed in a near-to-forward end
portion of the outer circumferential surface of the input-side
rotating shaft 1a and the second ball spline groove 6 formed in the
inner circumferential surface of the input-side disc 2a.
This assembling work is carried out upon the respective members as
shown in FIG. 5A in the state where the forward end portion of the
input-side rotating shaft 1a is placed on the lower side and the
input-side rotating shaft 1a is set to erect. Then, as shown by the
arrow .alpha., the balls 7 and 7 are inserted between the spline
grooves 5 and 6 from the opening portion (upper opening) on the
side of an inner end surface 59 of the input-side disc 2a and on
the side of the center of the input-side rotating shaft 1a.
Accordingly, to carry out the assembling work of the ball spline 4a
smoothly, the width of an upper end opening portion 61 of a space
60 surrounded by the spline grooves 5 and 6 has to be larger than
the diameter of each of the balls 7 and 7.
On the other hand, the opposite end portions of the first spline
groove 5 formed in a near-to-forward end portion of the outer
circumferential surface of the input-side rotating shaft 1a are
imperfect grooves 57 and 57 getting shallower gradually as shown in
FIG. 5A. The portion between the imperfect groove portions 57 and
57 is an effective groove portion 58 having a constant depth. When
the assembling work of the ball spline 4a is carried out without
compressing the coned disk spring 30 (hence with the coned disk
spring 30 left free) as shown in FIG. 5A, the inner end surface 59
of the input-side disc 2a is located comparatively closely to the
center of the input-side rotating shaft 1a. In this state, when the
axial position of the inner end surface 59 is located over the
imperfect groove portion 57 as shown in FIGS. 5A and 6, the width W
of the upper end opening portion 61 of the space 60 becomes smaller
than the diameter D of each of the balls 7 and 7 (W<D). Thus,
the work of inserting the balls 7 and 7 cannot be carried out.
Even in this case, when the input-side disc 2a is displaced toward
the forward end of the input-side rotating shaft 1a while
compressing the coned disk spring 30 elastically as shown in FIG.
5B, the inner end surface 59 can be moved to the effective groove
portion 58 of the first spline groove 5. Thus, the work of
inserting the balls 7 and 7 can be carried out. However, large
force, for example, about 9.8 kN (1 tf) is required for compressing
the coned disk spring 30. It is therefore troublesome to carry out
the work of inserting the balls 7 and 7 while compressing the coned
disk spring 30. Thus, cost required for the assembling work is
increased undesirably.
SUMMARY OF THE INVENTION
A toroidal type continuously variable transmission according to the
invention was developed in consideration of such circumstances.
It is an object of the invention to provide a toroidal type
continuously variable transmission in which balls constituting a
ball spline can be incorporated easily.
To attain the foregoing object, a toroidal type continuously
variable transmission according to the invention includes a
rotating shaft, a first disc, a second disc, a plurality of
trunnions, displacement shafts, power rollers, a hydraulic pressing
unit, a preload spring, and a ball spline.
The first disc has an inner side surface and is supported around
the rotating shaft displaceably in an axial direction of the
rotating shaft and rotatably in sync with the rotating shaft.
The second disc has an inner side surface opposed to the inner side
surface of the first disc. The second disc is disposed
concentrically with the first disc and rotatably independently of
the first disc.
The trunnions are provided between the first and second discs so as
to swing around pivot shafts located in screw positions with
respect to central axes of the two discs, respectively.
The displacement shafts project from inner side surfaces of the
trunnions.
The power rollers are sandwiched between the inner side surfaces of
the two discs so as to be supported on the displacement shafts
rotatably, respectively.
The hydraulic pressing unit is provided between the rotating shaft
and the first disc and for pressing the first disc toward the
second disc in accordance with pressure oil fed to the pressing
unit.
The preload spring is provided between the rotating shaft and the
first disc and for pressing the first disc toward the second disc
even when the pressing unit is not operated.
The ball spline supports the first disc displaceably in the axial
direction of the rotating shaft and rotatably in sync with the
rotating shaft.
Particularly, in the toroidal type continuously variable
transmission according to the invention, the ball spline includes a
first spline groove, a second spline groove, and balls. The first
spline groove is formed in an outer circumferential surface of the
rotating shaft. The second spline groove is formed in an inner
circumferential surface of the first disc. The balls are provided
between the first spline groove and the second spline groove
rollably.
Further, an axial position of an end portion of an effective groove
portion of the first spline groove is located to correspond to an
axial position of an inner end portion of the second spline groove
or more closely to the second disc than the axial position of the
inner end portion when the pressing unit, the preload spring and
the first disc are installed around the rotating shaft, pressure
oil is not fed to the pressing unit, and the preload spring is not
elastically deformed.
The hydraulic pressing unit may include at least one piston
member.
In the toroidal type continuously variable transmission configured
thus according to the invention, balls constituting a ball spline
can be incorporated easily between a first spline groove formed in
the outer circumferential surface of a rotating shaft and a second
spline groove formed in the inner circumferential surface of a
first disc particularly without compressing a preload spring.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are main portion sectional views showing an
embodiment of the invention, FIG. 1A showing the state in which a
preload spring is left free, FIG. 1A showing the state in which the
preload spring is compressed;
FIG. 2 is an enlarged view of portion A of FIG. 1A;
FIG. 3 is a sectional view of an example of the basic configuration
of a toroidal type continuously variable transmission known broadly
in the related art;
FIG. 4 is a sectional view showing an example of the structure of a
toroidal type continuously variable transmission in the related
art;
FIGS. 5A and 5B are sectional views showing a main portion in
association with the invention extracted from the structure shown
in FIG. 4, FIG. 5A showing the state in which a preload spring is
left free, FIG. 5B showing the state in which the preload spring is
compressed; and
FIG. 6 is an enlarged view of portion B of FIG. 5A.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1A and 1B and FIG. 2 show an embodiment of the invention.
Incidentally, this embodiment has a feature in that the dimensions
of a first spline groove 5 formed in the outer circumferential
surface of the forward end portion of an input-side rotating shaft
1a which is a rotating shaft is regulated by the relationship to an
input-side disc 2a which is a first disc, when the work of
inserting balls 7 and 7 between the first spline groove 5 and a
second spline groove 6 formed in the inner circumferential surface
of the input-side disc 2a is to be made easy. The configurations
and operations of the other members are similar to those in the
structure shown in FIG. 4. Therefore, illustration and description
about those equivalent members will be omitted or simplified, and
characteristic portions of the invention will be described chiefly
below.
As shown in FIG. 1A, constituent members of a hydraulic pressing
unit 34 assembled in advance in order to assemble a toroidal type
continuously variable transmission, that is, a cylinder 36, first
and second piston members 38 and 41, and a coned disk spring 30 are
outer-fitted to the inside of an outward flange portion 35 in the
forward end portion of the input-side rotating shaft 1a. Further,
the input-side disc 2a is outer-fitted to a near-to-forward end
portion of the input-side rotating shaft 1a, while the outer
circumferential edge portion of the input-side disc 2a is
inner-fitted to the cylinder 36. In this state, pressure oil is not
fed to first and second oil pressure chambers 44 and 45 of the
pressing unit 34, and the coned disk spring 30 is left free without
being compressed. Accordingly, the input-side disc 2a is displaced
(pushed upward) to the central portion of the input-side rotating
shaft 1a by the elastic force of the coned disk spring 30. After
the respective members 1a, 36, 38, 41 and 30 have been assembled as
shown in FIG. 1A, balls 7 and 7 constituting a ball spline 4a for
supporting the input-side disc 2a on the input-side rotating shaft
1a are incorporated between a first spline groove 5 formed in a
near-to-forward end portion of the outer circumferential surface of
the input-side rotating shaft 1a, and a second spline groove 6
formed in the inner circumferential surface of the input-side disc
2a.
In order to form the ball spline 4a in the state where the
respective constituent members have been assembled as shown in FIG.
1A in the case of the toroidal type continuously variable
transmission according to the invention, the axial position .alpha.
of the end portion (border between an effective groove portion 58
and an imperfect groove portion 57) of the effective groove portion
58 of the first spline groove 5 formed in the outer circumferential
surface of the input-side rotating shaft 1a is located more closely
to the center (upper side in FIG. 1) of the input-side rotating
shaft 1a than the axial position of an inner end surface 59 of the
input-side disc 2a corresponding to the inner end portion of the
second spline groove 6 formed in the inner circumferential surface
of the input-side disc 2a, as shown in FIG. 2.
Incidentally, assume that a large thrust load toward the forward
end portion of the input-side rotating shaft 1a is applied to the
input-side disc 2a so that the coned disk spring 30 is compressed
and brought into the state of completion of assembling the toroidal
type continuously variable transmission (the state where the
circumferential surfaces of the power rollers 22 and 22 have been
pressed onto the input-side inner side surface 3 of the input-side
disc 2a as shown in FIG. 4), as shown in FIG. 1B. In this case, the
inner end surface 59 of the input-side disc 2a corresponding to the
inner end portion of the second spline groove 6 is located around a
near-to center portion of the effective groove portion 58 of the
first spline groove 5. In this state, the axial distance between
the end portion of the effective groove portion 58 and the inner
end surface 59 is L.sub.1. This axial distance L.sub.1 is larger
than the compressed width of the coned disk spring 30, that is, a
stroke L.sub.2 of the input-side disc 2a between the state where
the coned disk spring 30 is left free and the state where the
assembling is completed (L.sub.1>L.sub.2).
At any rate, in the case of the toroidal type continuously variable
transmission according to this embodiment, the inner end surface 59
of the input-side disc 2a is located around the effective groove
portion 58 of the first spline groove 5 in the state where the
coned disk spring 30 is left free, that is, in the state where the
input-side disc 2a is displaced closely to the center of the
input-side rotating shaft 1a by the coned disk spring 30.
Accordingly, width W.sub.a of an upper-end opening portion 61a of a
space 60 between the first spline groove 5 and the second spline
groove 6 becomes equal to the diameter D of each of the balls 7 and
7 or larger than the diameter D (W.sub.a.gtoreq.D). Thus, the work
of inserting the balls 7 and 7 into the space 60 can be carried out
easily.
Incidentally, in the illustrated embodiment, description has been
made on the case in which the pressing unit 34 having the first and
second piston members 38 and 41 installed is used so as to be
capable of generating large thrust compared with the diameter.
However, the invention may be applied to a hydraulic pressing unit
in which only one piston is incorporated. Further, the invention
may be applied to a single-cavity type toroidal type continuously
variable transmission as described above.
While only certain embodiments of the invention have been
specifically described herein, it will apparent that numerous
modifications may be made thereto without departing from the sprit
and scope of the invention.
Since the invention is configured and operated as described above,
surface pressures in contact portions between inner side surfaces
of input-side and output-side discs and circumferential surfaces of
power rollers can be adjusted rapidly into optimum values in
accordance with running conditions. In addition, since the work of
assembling a small-size and light-weight toroidal type continuously
variable transmission is made easy, the invention can contribute to
realization of such a toroidal type continuously variable
transmission.
* * * * *